1. Field of the Invention
The invention relates to electrical connectors and, more particularly, to EMI shielded connectors which include protection against harsh corrosive conditions.
2. Description of the Prior Art
Effective connectors should be mechanically strong, light weight, low cost, corrosion resistant and display high levels of EMI shielding. In general, good EMI shielding comes from metals. Aluminum and its alloys have always been good choices because they are lightweight, highly conductive and readily machined into parts. Unfortunately, aluminum is also chemically reactive and is prone to significantly corrode in harsh environments.
Because of the above problems, composite plastic materials have been employed to form the connector housing. Since plastic is non-conductive, fillers were used to provide some degree of EMI shielding. Great difficulty was incurred, however, in creating a sufficiently homogenous mixture of filler to provide effective shielding. This was because molding processes do not allow the necessary even distribution and physical contact between filler particles for achieving the desired overall conductivity.
An alternative to the composite plastic approach is shown in U.S. Pat. No. 4,678,260. Here, a foraminous sleeve of metal or wire mesh is embedded in the molded plastic housing. A portion of the sleeve is exposed to provide contact with other conductive parts which lead to a ground plane.
Difficulty with this approach is that sleeve openings or mesh size directly affect the frequency level of EMI that can be effectively attenuated. Such a restriction greatly limits the usefulness of the device.